A computational search for the zeta phase in the tantalum carbides. Issue 3 (14th August 2018)

• Record Type: Journal Article
• Authors: Weinberger, Christopher R.; Thompson, Gregory B.
• Is Part Of: Journal of the American Ceramic Society. Volume 102:Issue 3(2019)
• Page Start: 1454
• Page End: 1462
• Publication Date: 2018-08-14
• Subjects: carbides -- crystals/crystallization -- density functional theory -- phase equilibria; Ceramics -- Periodicals; 620.1405
• DOI: 10.1111/jace.15970
• Languages: English
• ISSNs: 0002-7820

Abstract

Abstract: A systematic electronic structure density functional theory search for the zeta phase in the tantalum carbon system has been conducted, demonstrating that the zeta phase does indeed lie on the convex hull, establishing low‐temperature thermodynamic stability, and is structurally stable. Even though the zeta phase is most oft reported as a R 3 ¯ m ζ‐Ta4 C3‐x structure, these new computational results reveal that the perfectly ordered zeta phase occurs at the Ta3 C2 composition and belongs to the C2/m space group. Furthermore, these results suggest that the R 3 ¯ m space group may be a result of an order‐disorder transition and potential deviations from ideal stoichiometry at higher temperatures. The structure of this Ta3 C2 compound can be described as ordered strings of carbon vacancies on a single carbon plane, which is also the preferred plane where additional carbon vacancies or interstitials form. These defects have modest formation energies, which provides further explanation for the small homogeneity range in zeta phase.